Reducing noise and flash from military and security personnel firearms (e.g., long guns and pistols) provides a significant tactical advantage in the field. For military personnel, reduced sound levels will also reduce associated hearing loss. Additionally, application of sound suppression to civilian firearms reduces the objectionable noise to area residents and when used for hunting, to other hunters. Suppressors do not “silence” the gunshot. Instead, they reduce the level of sound associated with the detonation of the propellant.
The blast characteristics of a gunshot include three core elements. The first two core elements are the precursor blast and the main blast set up by the expanding gases. The precursor blast consists mostly of air with a small amount of propellant, while the main blast consists of spherical pressure waves that quickly overtake the fired projectile. Both of these blasts are sources of low frequency noise that carry for long distances.
The third core element is a highly visible gas flash which follows the blasts. In general, flash phenomena occur in two ways. Ammunition propellant is typically fuel rich, leaving unburned powder in the exhaust gases. As these high-pressure exhaust gases leave the muzzle of the firearm, the flow immediately expands and a shock wave is formed. Typically, the expansion forms a small glowing cone immediately following the muzzle, then several diameters away a large disk like shock wave forms, known as the mach disk. In these two regions, temperature and pressure levels change almost instantly. These sudden energy changes cause the exhaust gases to radiate light, known as the primary and intermediate flash, respectively.
As the unburned powder travels through this mach disk, the sudden temperature spike, along with the presence of oxygen in the ambient air allow these gases to reignite, generating a significant amount of visual signature. This is known as secondary flash.
To minimize the flash and the percussive level, it is necessary to slow the gases exiting the muzzle. This, however, must be accomplished without degrading the accuracy of the firearm.